1. Field of the Invention
The present invention relates to a linear guide mechanism of an advancing/retracting mechanism incorporated in a photographing (imaging) lens (lens barrel).
2. Description of the Related Art
A double-sided cam ring which is provided on each of outer and inner peripheral surfaces thereof with at least one cam groove so that two movable elements which are respectively positioned inside and outside the cam ring are driven to advance or retract in different moving manners by rotation of the cam ring is often used as a fundamental element of a lens barrel such as a photographing lens. In this type of advancing/retracting mechanism, each of the two movable elements (the outer movable element and the inner movable element) which are respectively positioned outside and inside the cam ring needs to be guided in a direction parallel to the rotational axis of the cam ring. Conventionally, the advancing/retracting mechanism is provided around the cam ring with a linear guide member for guiding the outer movable element linearly along the rotational axis of the cam ring without rotating, while the outer movable element guides the inner movable element linearly along the rotational axis of the cam ring without rotating. Accordingly, this conventional linear guide structure is a single-guiding-path type, in which the linear guide member guides the inner movable element via the outer movable element. In this single-guiding-path linear guide structure, if the relative speed of movement between the outer movable element and the inner movable element is fast, excessive loads may be applied on the linear guide structure. Moreover, it is difficult to guide the inner movable element linearly along the rotational axis of the cam ring without rotating with a high degree of movement accuracy because there is no direct engagement between the linear guide ring and the inner movable element.